In the production of metals, it is common to produce heat for the refining process by passing electric current through a charge of ore to permit a refining chemical reaction to take place. Electric current is introduced into the charge through an electrode which is in contact with the charge.
The electrode typically contains carbon and is decomposed slowly at the region of contact with the charge, thus requiring it to be slowly advanced as the refining reaction progresses. Many electrode designs have been suggested to provide an electrode of adequate size and which can be advanced into the charge. One such design is known as a self-baking electrode. In this type of electrode, an essentially continuous electrode is formed by allowing an electrode paste to be heated to bake the paste into a hard electrode which will conduct electricity into the charge.
One such known self-baking electrode is shown in FIG. 1. A tubular steel casing 2 contains electrode paste in an upper portion. Fins 4 extend radially inwardly from casing 2 to provide additional area to engage and support the electrode paste. The casing is supported at its upper end by slipping bands 6 which are in turn supported by a hydraulic jack 8 resting on beams 10. Electric current is introduced at a conducting band 12 which receives current through a conductor 14. Band 12 is urged against the outside surface of casing 2 by pressure ring 16 which is supported by arms 18. The paste is baked in baking zone 20 by the heat generated by the passage of current to produce a baked electrode at 22. Current flows from conducting band 12 into the furnace charge to heat it. Slipping bands 6 operate to lower the casing and electrode during the refining process as the baked electrode 22 is consumed.
As the electrode of FIG. 1 is advanced, the steel casing and steel fins melt and contaminate the ore being refined. When the ore is iron, such as in steel making, such is not unacceptable. On the other hand, in the making of other metals, such as silicon, the addition of iron is highly objectionable and severely limits the use toi which the electrode of FIG. 1 can be put in the production of silicon and other non-ferrous metals.
FIG. 2 shows another prior art self-baking electrode. A casing 24 is tubular and encloses paste 26. Vertical support is provided by a steel cable 28 having a plurality of steel bars 30 extending transversely through the cable to engage and support the unbaked paste. Slipping shoes 32 engage the outer surface of casing 24 to advance the electrode into the charge. Current is applied through conducting ring 34, and a baked electrode 36 is produced at the lower end.
Cable 28 is supported by a mechanism (not shown) which allows the center part of the electrode to be advanced at a rate faster than the advancement of the outer casing. In a typical installation, the inner electrode is advanced at a rate as much as 12 times greater than that of the outer casing.
The electrode of FIG. 2 has many disadvantages, such as the unstable control of the electrode due to the stretching of the steel cable and the contamination of the metal being refined by the melting of the steel cable and steel bars.
FIG. 3 is another example of a prior art self-baking electrode. An outer casing 38 encloses unbaked paste 40, and a graphite support electrode 42 extends along the length of the electrode to support the central electrode. In a manner similar to that described with respect to FIG. 2, the center electrode is advanced at a rate up to 12 times the rate of advancement of the outer casing. The outer casing is supported and advanced by shoes 44. Electricity is introduced at a conducting ring 46, and a baked electrode 48 is formed.
While the electrode of FIG. 3 does not suffer from the contamination problems discussed with respect to the electrodes of FIGS. 1 and 2, it is not practical to make the electrode of FIG. 3 in sufficient size for many furnaces in use today. The graphite support electrodes are typically machined from solid graphite, and electrodes of adequate diameter to produce a self-baking electrode of size sufficient to support commercial production of metal are extremely expensive.
U.S. Pat. No. 1,442,031 (Soderberg) shows yet another self-baking electrode. In this arrangement, a baked electrode portion is engaged by a support element, and a casing extending above the baked portion supports un-baked paste. The un-baked paste becomes baked by contact with heat from the furnace. In an embodiment shown in FIG. 2 of the Soderberg patent, electricity is introduced into the baked portion of the electrode through a centrally-located conductor. This electrode was never commercially successful and would suffer from several problems. For example, the only baking energy is from the furnace which would result in inadequate baking and would require a baked portion of substantial length.
Other prior art self-baking electrodes are shown in U.S. Pat. Nos. 3,524,004 (Van Nostran, et al.) and 1,640,735 (Soderberg).